Question

What is the role of nitric oxide in the learning process?

Answer 1

• Nitric oxide (NO) which is a gas made up of two most common gases in the atmosphere, occurs in the biological system. NO crosses cell membranes freely and plays a role as a neurotransmitter in the brain.
• The function of NO in the hypothalamus has largely been implicated in learning process and in memory formation.
• NO formed in the hippocampus has been suggested to have a role in learning and memory processes because the activity of NMDA receptor which is an initiator of the reaction that produces NO from L-arginine.
• Since neuronal NO has a very short half-life (5 sec), the level of its metabolite, nitrite or the activity of NOS has been measured in the hippocampus of animals during learning process.
• Learning of spatial task by rats was found to be accompanied by an elevation of nitrite in the hippocampus. The activity of NOS was found to be increased by 45 per cent in the hippocampus immediately after acquisition of an avoidance task in rats.
• Further, spatial memory was accompanied by an increase in the activity of NOS in the hippocampus of rats. These findings and an increased expression of nNOS in the hippocampus during learning of odour in sheep and in mice provide evidence for a correlation between learning process and an activation of nNOS in the hippocampus.
• The experimental findings reviewed provide sufficient evidence that NO activates the computational ability of the brain. These findings provide sufficient support to the report that L-arginine, the precursor and donor of NO may play a prominent role in the treatment of age-related degenerative disease. L-arginine and NO donors may also be effective in preventing cognitive disorder produced by epilepsy, antiepileptic drugs, and diabetes.
• The role of nitric oxide on passive avoidance learning was studied by administering l-arginine or d-arginine to male rats in a passive avoidance paradigm.
• The results indicate that nitric oxide is able to facilitate the learning and consolidation of memory in a passive avoidance paradigm, but it is ineffective in retrieval processes.
• The results also suggest that, under the experimental circumstances used, nitric oxide is involved only in the facilitated learning and memory processes caused by pharmacological effect of l-arginine, and not involved in normal learning processes.